1. Field of the Invention
The present invention relates to a meteorological radar system that detects and observes moving objects.
2. Description of the Related Art
In meteorology, radar is used to gather information related to atmospheric phenomena through a process of transmitting electromagnetic waves which is scattered by objects, such as water droplets distributed in the air due to certain atmospheric phenomena, and receiving the scattered echoes. An ordinary meteorological radar system, for example, searches a circular area by rotatably sweeping its azimuth. CAPPI (Constant Altitude Plan Position Indicator) scanning is exemplified as a method of observing the weather conditions within a half spherical observation area. In CAPPI scanning, the search radar antenna transmits and receives beams at different elevation angles and at different angles in azimuth by performing both a rotational scanning operation in azimuth and an elevation angle varying operation. For example, in this scanning operation, each time the antenna is rotated once in its azimuth, the altitude is sequentially changed by a certain angle.
For meteorological study purposes, the radar equipment can fully work by scanning with only the area where atmospheric phenomena to be detected exist. Therefore, by setting the radar scanning range according to the location of atmospheric phenomena and the space area, an observer can observe an object with higher resolution than is possible with observation over all directions and all ranges.
In order to detect moving objects (e.g. fog or thundercloud) which may occur at any arbitrary point in an observation area, a conventional meteorological radar system such as described above must scan the entire observation area by continuously scanning its antenna in all angles in the azimuth and in wide range of elevation angles, without regard to the presence or absence of an object.
However, a conventional radar system has a disadvantage in that it requires a large time to observe all observation areas, thus deteriorating the time resolution for observation.
Further problem is that the CAPPI scanning operation generally degrades the space resolution at certain elevation angles because observations at selected elevation angles are skipped to reduce the time required for one CAPPI operation period.
Furthermore, this type of meteorological radar system has a disadvantage in that, when the observation area in the radius direction is set to a wider range, the space resolution remarkably decreases for observation areas distant from the location of the meteorological radar system because it largely diverges in the direction perpendicular to the line of sight.
A decrease in space resolution makes it difficult to observe in detail the internal structure of atmospheric phenomena, so that it becomes impossible to provide a precise weather forecast or report.
One approach to deal with the above-mentioned problems has been to use a meteorological radar system employing a RHI (Range Height Indicator) scanning operation (hereinafter referred to as RHI meteorological radar). However, this approach has a disadvantage in that the limited observation range of the meteorological radar system makes it impossible to observe other atmospheric phenomena which may occur outside of the observation range.